1. Field of the Invention
The present invention relates generally to the optical transmission of information and, more particularly, to systems and techniques for improving transmission capabilities over long haul optical fiber transmission systems.
2. Description of the Background Art
Technologies used in long haul optical fiber communication networks, as an example, those employed in undersea systems, have changed radically over the last decade, driven primarily by the emergence of the erbium doped fiber amplifier (EDFA). EDFA""s have enabled long, transoceanic systems to offer significantly higher capacities (tens to hundreds of gigabits per second per fiber pair) and much longer lengths in repeaterless systems. As this evolution has occurred, many nations have begun to appreciate the benefits of becoming totally involved with the burgeoning global economy, and have realized that such participation requires a fiber-optic communication to world markets. Finally, the explosive growth of packetized traffic driven by the Internet has touched off an accelerated need to plan and implement undersea optical fiber communication networks capable of handling the exchange of huge volumes of data over long distances.
For over a decade, transmission performance in telecommunications systems has been measured by the standards of the International Telecommunications Union (ITU). The network interface of greatest interest for undersea networks has been, since around 1990, the 155 Mbits/s optical and electrical signal interface of the synchronous digital hierarchy (SDH) synchronous transfer module defined by the ITU-T standards. Use of the SDH standards has simplified the interconnection of networks owned by different entities with equipment purchased from a multitude of vendors.
For packetized traffic transported by means of conventional undersea SDH transport techniques, it will be appreciated by those skilled in the art that protection against fiber breaks and cable faults may be achieved by incorporating redundant fiber links. In the long-haul network 10 depicted in FIG. 1, illustratively an undersea network incorporating spans of fiber exceeding 2000 km, redundancy is implemented using a single or double pair of fibers in a bi-directional line switched ring configuration. With continued reference to FIG. 1, it will be seen that long-haul network 10 incorporates four terminal or xe2x80x9clandingxe2x80x9d stations indicated generally at 12, 14, 16, and 18 respectively. Within each terminal station, SDH multiplexing/demultiplexing equipment 20 is provided for accepting and aggregating voice and data traffic from multiple subscribers (not shown). In accordance with a bandwidth provisioning contract made with the owner or operator of network 10, each such subscriber, illustratively an internet service provider is (ISP), supplies a stream of voice or data traffic at an agreed upon SDH transmission rate as, for example, 155 Mb/s, 622 Mb/s or 2.5 Gb/s.
In addition to the SDH multiplex/demultiplex equipment 20, the other terminal transmission equipment utilized in the conventional undersea communication system of FIG. 1 includes line terminating equipment or units (LTU""s) 22, order wire equipment, switches and bridges, and monitoring and control circuitry. In combination, these devices have accommodated a number of architecture and networking options, including the most widely used add/drop line switched ring-protected configuration shown in FIG. 1. In the network of FIG. 1, the stations are interconnected by multiple fiber pairs, each fiber pair 24a-24d extending between respective LTUs. In the network topology of FIG. 1, which as will be recalled is chosen to achieve the high reliability generally demanded by subscribers, it will be readily appreciated by those skilled in the art that the distinction between xe2x80x9cworkingxe2x80x9d and xe2x80x9cprotectionxe2x80x9d fibers translates into only fifty percent of the nominally available transmission capacity being made available to subscribers for carrying transmission capacity that can be protected against failures.
Thus, while the reliability afforded by the ring topology is extremely high, it can not be flexibly reconfigured to match the needs of certain classes of subscribers, internet service providers (ISP""s) for example, who would readily accept a lower level of redundancy in exchange for the ability to exchange more traffic over the long-haul xe2x80x9cbottleneckxe2x80x9d that may lie between two communication networks. Accordingly, there exists a need for a long haul optical fiber communications network capable of efficiently utilizing all of the available transmission capacity while still retaining the ability to supply each subscriber with a level of service flexibly tailored to that subscriber""s expectations of reliability and available capacity.
The aforementioned deficiencies are addressed, and an advance is made in the art by a system and method for exchanging packets via a long-haul optical fiber communication network. Packets are received at a first boundary node of a long haul optical communication network which may either interconnect originating and destination communication networks or form an integral part of a single end-to-end network. Packets are reclassified to reflect a higher priority of transmission than non-long haul bound packets, as by marking them with an indication of a modified priority level of transmission. Reclassified packets are transmitted over a long-haul optical link to a second boundary node. So that the modified priority level employed in the long-haul network may be understood by a destination network, packets arriving at the second boundary node may be re-mapped or reclassified to a value recognized as being of at least equal and, preferably, higher priority than that originally established by the originating network and/or first boundary node. Using a substantially equal priority value in the reclassification establishes at least a consistent, end-to-end quality of service for each packet that has traversed the long haul portion of a communications network. More efficient use of transmission resources is realized by associating a higher priority with packets that have traversed the long haul portion of the network, each packet increasing in value as it nears the ultimate destination. Essentially, the reclassification decreases the likelihood that a packet, having made such substantial progress as to have traversed the length of the long haul portion of the network, will be dropped prior to reaching its destination and require re-transmission.
Advantageously, the priority classification scheme of the present invention also permits different classes of service to be defined. Long haul optical fiber communication networks, especially long haul undersea optical fiber communication networks, typically interface many different ISP domains with heterogeneous application requirements. Utilizing a packet classification scheme permits the long haul network owner or operator to not only accommodate these differing application requirements, but also to offer flexible pricing. By way of illustration, this may be achieved in an IP traffic carrying network by configuring the boundary router to evaluate a field in the packet header in conjunction with the source port address. By employing long haul boundary routers having such functionality, the owner or operator of the long haul network may, for example, sell a certain amount of capacity as xe2x80x9cguaranteedxe2x80x9d or xe2x80x9cpremiumxe2x80x9d class transmission servicesxe2x80x94corresponding to that portion of the network which can be reliably served (e.g., that capacity which would otherwise have been provided, for example, by the xe2x80x9cworking fiberxe2x80x9d in the conventional topology of FIG. 1. Additional capacity may be sold to ISP networks and other data communication networks in accordance with an xe2x80x9cassured servicesxe2x80x9d contract for transmission services. The entire capacity may again be sold to still other data communication networks in accordance with a contract for xe2x80x9cbest effortxe2x80x9d services. In this manner, service is pledged to those subscribers willing to pay, while others can contract for whatever capacity is left over when and as it becomes available.
At the first boundary node or router, packets arriving from the first data communication network are examined to determine the destination port address. Advantageously, most or all of the processing resources of the boundary router are reserved for traffic to be routed via the long-haul network to which the boundary router is connected. That is, segmentation is achieved between, on the one hand, the long haul optical fiber communication network itself, and on the other hand, the data communications networks connected thereto such, for example, as the first and second data communication networks. By way of illustration, this may be achieved in an IP traffic carrying network by assigning at least one of a plurality of interfaces of a source boundary router to at least the particular IP address associated with the second data communication network. Still others of the interfaces of the source boundary router may be assigned to respective IP addresses associated with other data communication networks with which interconnectivity is to be established by the long haul network. In such an illustrative arrangement, the aforementioned segmentation is achieved by configuring the router to examine the destination address of each packet received via the first plurality of interfaces and dropping those packets which do not match an IP address associated with one of the second plurality of interfaces. Alternatively, multiple queues may be established in which packets requiring routing via the long haul network are given preferential treatment over those which do not require such routing. It should be pointed out that the segmentation aspect of the present invention does not require the use of the plural groups of interfaces capable of transmitting at respectively different line rates. That is, although the inventive aspects of segmentation and efficient capacity utilization in a long haul boundary router are mutually desirable, they do not depend upon one another for their implementation.